Kallmann syndrome

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Kallmann syndrome
Video explanation
Specialty Endocrinology

Kallmann syndrome (KS) is a genetic disorder that prevents a person from starting or fully completing puberty. If left untreated people with Kallmann syndrome will have poorly defined secondary sexual characteristics, show signs of hypogonadism, almost invariably be infertile and be at increased risk of developing osteoporosis.[1] A range of other physical symptoms affecting the face, hands and skeletal system can also occur.

The underlying cause is a failure in the correct production of the GnRH hormone by the hypothalamus. This results in low levels of the sex hormones testosterone in males or oestrogen and progesterone in females. Diagnosis normally occurs during teenage years when puberty fails to start. Kallmann syndrome is a form of a group of conditions termed hypogonadotropic hypogonadism. Kallmann syndrome has an additional symptom of a total lack of sense of smell or a reduced sense of sense of smell which distinguishes it from other forms of hypogonadotropic hypogonadism.[1]

Treatment for both males and females is normally required life long. Hormone replacement therapy (HRT) is the major form of treatment with the aim to replace the missing testosterone or oestrogen and progesterone. Specialised fertility treatments are also available.[2][3][4]

A 2011 study of the Finnish population produced an estimated incidence of 1 in 48,000 people overall, with 1 in 30,000 for males and 1 in 125,000 for females.[5] The condition is more commonly diagnosed in males than in females.[6] Kallmann syndrome was first described by name in a paper published in 1944 by Franz Josef Kallmann, a German-American geneticist.[7][8] The link between anosmia and hypogonadism had already been noted by the Spanish doctor Aureliano Maestre de San Juan in 1856.[9]

Signs and symptoms[edit]

It is normally difficult to distinguish a case of KS / HH from a straightforward constitutional delay of puberty. However, if puberty has not started by either age 14 (girls) or 15 (boys) and one or more of the non-reproductie features mentioned belowe is present then a referral to reproductive endocrinologist might be advisable.[10][1][6]

The features of Kallmann syndrome (KS) and other forms of hypogonadotropic hypogonadism (HH) can be split into two different categories; "reproductive" and "non reproductive".[3][11][4][12][2]

Reproductive features[edit]

Non-reproductive features[edit]

  • Total lack of sense of smell (anosmia) or markedly reduced sense of smell (hyposmia). This is the defining feature of Kallmann syndrome; it is not seen in other cases of HH. Approximately 50% of HH cases occur with anosmia and can be termed as Kallmann syndrome.[2]
  • Cleft palate, hare lip or other midline cranio-facial defects.[3]
  • Neural hearing impairment[2]
  • Absence of one of the kidneys (unilateral renal agenesis)[2]
  • Skeletal defects including split hand/foot (ectrodactyly), shortened middle finger (metacarpal)[2] or scoliosis[13]
  • Manual synkinesis (mirror movements of hands)[2]
  • Missing teeth (hypodontia)[2]
  • Poor balance or coordination due to cerebral ataxia.[6]
  • Eye defects such as coloboma or ptosis.[11]

The exact genetic nature of each particular case of KS / HH will determine which, if any, of the non-reproductive features will occur. The severity of the symptoms will also vary from case to case. Even family members will not show the same range or severity of symptoms.[2][6]

KS / HH is most often present from birth but adult onset versions are found in both males and females. The hypothalamic-pituitary-gonadal axis (HPG axis) functions normally at birth and well into adult life giving normal puberty and normal reproductive function. The HPG axis then either fails totally or is reduced to a very low level of GnRH release, in adult life with no obvious cause such as a pituitary tumour. This will lead to a fall in testosterone or oestrogen levels and infertility.[13][14]

Functional hypothalamic amenorrhoea is seen in females where the HPG axis is suppressed in response to physical or psychological stress or malnutrition. It is reversible with the removal of the stressor.[1]

Some cases of KS / HH appear to reverse during adult life where the HPG axis resumes its normal function and GnRH, LH, and FSH levels return to normal levels. This occurs in an estimated 10 to 20% of people, primarily normosmic CHH cases rather than KS cases and only found in people who have undergone some form of testosterone replacement therapy. It is only normally discovered when testicular volume increases while on testosterone treatment alone and testosterone levels return to normal when treatment is stopped. This type of KS / HH rarely occurs in cases where males have had a history of un-descended testes.[6][3]

Affected individuals with KS and other forms of HH are almost invariably born with normal sexual differentiation; i.e., they are physically male or female. This is due to the human chorionic gonadotrophin (hCG) produced by placenta at approximately 12 to 20 weeks gestation (pregnancy) which is normally unaffected by having KS or CHH.[15]

People with KS / HH lack the surge of GnRH, LH, and FSH that normally occurs between birth and six months of age. This surge is particularly important in infant boys as it helps with testicular descent into the scrotum. The surge of GnRH/LH/FSH in non KS/HH children gives detectable levels of testosterone in boys and oestrogen & progesterone in girls. The lack of this surge can sometimes be used as a diagnostic tool if KS / HH is suspected in a newborn boy, but is not normally distinct enough for diagnosis in girls.[3]


One possible side effect of having KS/CHH is the increased risk of developing secondary osteoporosis or osteopenia. Oestrogen (females) or testosterone (males) is essential for maintaining bone density.[16] Deficiency in either testosterone or oestrogen can increase the rate of bone resorption while at the same time slowing down the rate of bone formation. Overall this can lead to weakened, fragile bones which have a higher tendency to fracture.

Even a short time with low oestrogen or testosterone, as in cases of delayed diagnosis of KS/CHH can lead to an increased risk of developing osteoporosis but other risk factors, such as smoking are involved so the risk of developing it will vary from person to person. Bone density scans are recommended to monitor the bone mineral density.[13]

The bone density scan is known as a dual energy X-ray absorptiometry scan (DEXA or DXA scan). It is a simple test, taking less than 15 minutes to perform. It involves taking a specialised X-ray picture of the spine and hips and measuring the bone mineral density and comparing the result to the average value for a young healthy adult in the general population.[17]

Adequate calcium levels, and probably more importantly vitamin D levels are essential for healthy bone density. Some people with KS/CHH will have their levels checked and may be prescribed extra vitamin D tablets or injections to try to prevent the condition getting worse. The role of vitamin D for general overall health is under close scrutiny at the moment with some researchers claiming vitamin D deficiency is prevalent in many populations and can be linked to other disease states.[18]

Some people with severe osteoporosis might be prescribed bisphosphonates to preserve bone mass in addition to hormone replacement therapy.[19]


The genetic and molecular basis of idiopathic hypogonadotropic hypogonadism

To date at least twenty five different genes have been implicated in causing Kallmann syndrome or other forms of hypogonadotropic hypogonadism through a disruption in the production or activity of GnRH. These genes involved cover all forms of inheritance and no one gene defect has been shown to be common to all cases which makes genetic testing and inheritance prediction difficult.[20][21]

The number of genes known to cause cases of KS / CHH is still increasing.[12] In addition it is thought that some cases of KS / CHH are caused by two separate gene defects occurring at the same time.[6]

Table of known genes responsible for cases of Kallmann syndrome and other forms of hypogonadotropic hypogonadism. Listed are the estimated prevalence of cases caused by the specific gene, additional associated symptoms and the form of inheritance.[6][2]Between 35-45% of cases of KS / CHH have an unknown genetic cause.[22]

Prevalence (%) OMIM Name Gene Locus Clinical features Syndromes Associated Inheritance pattern
5[6], 5-10[2] 308700 KAL1 (ANOS1) KAL1 Xp22.3 Anosmia. Bimanual synkinesis. Renal agenesis. x-linked
10[6][2] 147950 KAL2 FGFR1 8p11.23 Cleft lip and / or cleft palate. Septo-optic dysplasia. Skeletal anomomalies. Bimanual synkinesis. Hand / foot malformations such as ectrodactyly. Combined pituitary hormone deficiency. Hartsfield syndrome Autosomal dominant
6-16[6], 5-10[2] 146110 GNRHR GNRHR 4q13.2 Autosomal recessive
6[6], 5-10[2] 612370 CHD7 CHD7 8q12.2 Congenital hearing loss. Semicircular canal hypoplasia. CHARGE syndrome Autosomal dominant
3-6[6], <2[2] 610628 KAL4 PROK2 3p13 Autosomal recessive
3-6[6], 5[2] 244200 KAL3 PROKR2 20p12.3 Combined pituitary hormone deficiency. Morning Glory syndrome Autosomal recessive
3[6], 2-5[2] 615267 IL17RD IL17RD 3p14.3 Congenital hearing loss. Autosomal recessive
2[6], 2-5[2] 611584 SOX10 SOX10 22q13.1 Congenital hearing loss. Waardenburg syndrome Autosomal dominant
2[6], <2[2] 614842 KISS1 KiSS-1 1q32.1 Autosomal recessive
2[6], <2[2] 614837 KISS1R (GPR54) GPR54 19p13.3 Autosomal recessive
<2[2] 612702 FGF8 FGF8 10q24.32 Cleft lip and / or cleft palate. Skeletal anomomolies. Bimanual synkinesis. Combined pituitary hormone deficiency. Autosomal dominant
<2[6], 1 report[2] 615270 FGF17 FGF17 8p21.3 Dandy-Walker syndrome Autosomal dominant
<2[6] 164260 LEP LEP 7q32.1 Early onset of morbid obesity. Autosomal recessive
<2[6] 601007 LEPR LEPR 1p31.3 Early onset of morbid obesity. Autosomal recessive
<2[6] 162150 PCSK1 PCSK1 5q15 Early onset of morbid obesity. Autosomal recessive
Rare[6], 1 report[2] 616030 FEZF1 FEZF1 7q31.32 Autosomal recessive
Rare[6], 1 report[2] 616031 CCDC141 CCDC141 2q31.2 Unknown
Rare[6], <2[2] 614897 SEMA3A SEMA3A 7q21.11 Autosomal dominant
1 report[2] 608166 SEMA3E SEMA3E 7q21.11 CHARGE syndrome Autosomal dominant
Rare[6] 607961 SEMA7A SEMA7A 15q24.1 Autosomal dominant
Rare[6], <2[2] 614880 HS6ST1 HS6ST1 2q14.3 Cleft lip and / or cleft palate. Skeletal anomalies. Autosomal dominant
Rare[6], 1 report[2] 614858 WDR11 WDR11 10q26.12 Combined pituitary hormone deficiency. Autosomal dominant
Rare[6] 614838 NELF (NSMF) NELF 9q34.3 Autosomal dominant
Rare[6] 617351 IGSF10 IGSF10 3q24 Autosomal dominant
Rare[6], <2[2] 614841 GNRH1 GNRH1 8p21.2 Autosomal recessive
Rare[6], <2[2] 614839 TAC3 TAC3 12q3 Autosomal recessive
Rare[6], 5[2] 614840 TACR3 TACR3 4q24 Autosomal recessive
Rare[6] 611744 OTUD4 OTUD4 4q31.21 Cerebellar ataxia. Gordon Holmes syndrome Autosomal recessive
Rare[6] 609948 RNF216 RNF216 7p22.1 Cerebellar ataxia. Gordon Holmes syndrome Autosomal recessive
Rare[6] 603197 PNPLA6 PNPLA6 19p13.2 Cerebellar ataxia. Gordon Holmes syndrome Autosomal recessive
1 report[2] 109135 AXL AXL 19q13.2 Unknown
Rare[6] 612186 DMXL2 DMXL2 15q21.2 Polyendocrine deficiencies and polyneuropathy. Autosomal recessive
Rare[6] 300473 NR0B1 (DAX1) NR0B1 Xp21.2 Adrenal hypoplasia. x-linked
1 report[2] 602748 DUSP6 DUSP6 12q21.33 Autosomal dominant
1 report[2] 614366 POLR3B POLR3B 12q23.3 Autosomal recessive
1 report[2] 615266 SPRY4 SPRY4 5q31.3 Autosomal dominant
1 report[2] 615271 FLRT3 FLRT3 20p12.1 Autosomal dominant
1 report[2] 617264 SRA1 SRA1 19q13.33 Unknown
Rare[6] 601802 HESX1 HESX1 3p14.3 Septo-optic dysplasia. Combined pituitary hormone deficiency. Autosomal recessive and dominant


Shows the normal hormonal control of puberty from the hypothalamus down to the testes or ovaries and their negative feedback mechanisms. The negative feedback control allows just the right amount of hormone to be released according to the needs of the body at that time.
Shows the effect of the interruption of GnRH hormone release from the hypothalamus on the subsequent inability of the testes and ovaries to function correctly at puberty as seen in cases of KS/HH. In most cases of KS/HH the testes and ovaries are able to function correctly, but fail to do so because they have not had the correct hormonal signals.
The structure of GNRH1
(from PDB: 1YY1​)

The underlying cause of Kallmann syndrome or other forms of hypogonadotropic hypogonadism is a failure in the correct action of the hypothalamic hormone GnRH. This failure in GnRH activity can either be due to the absence of the GnRH releasing neurones inside the hypothalamus or the inability of the hypothalamus to release GnRH in the correct pulsatile manner to ensure LH and FSH release from the pituitary.[12][22] HH can occur as an isolated condition with just the LH and FSH production being affected or it can occur in combined pituitary deficiency conditions.

The term isolated GnRH deficiency (IGD) has increasingly been used to describe this group of conditions as it highlights the primary cause of these conditions and distinguishes them from other conditions such as Klinefelter syndrome or Turner syndrome which share some similar symptoms but have a totally different etiology.[23] The term hypogonadism describes a low level of circulating sex hormones; testosterone in males and oestrogen and progesterone in females. Hypogonadism can occur through a number of different mechanisms. The use of the term hypogonadotropic relates to the fact that the hypogonadism found in HH is caused by a disruption in the production of the gonadotropin hormones normally released by the anterior pituitary gland known as luteinising hormone (LH) and follicle stimulating hormone (FSH).

In the first 10 weeks of normal embryonic development the GnRH releasing neurones migrate from their original source in the nasal region and end up inside the hypothalamus. These neurones originate in an area of the developing head, called the olfactory placode, that will give rise to the nose; they then pass through the cribriform plate, along with the fibres of the olfactory nerves, and into the rostral forebrain. From there they migrate to what will become the hypothalamus. Any problems with the development of the olfactory nerve fibres will prevent the progression of the GnRH releasing neurones towards the brain.[24]


The diagnosis is often one of exclusion found during the workup of delayed puberty.[25][26][27]

One of the biggest challenges in the diagnosis of KS and other forms of CHH is the ability to distinguish between a normal constitutional delay of puberty or a case of KS / CHH[28][4][29]

Post natal diagnosis of KS / CHH before the age of 6 months is sometimes possible. The normal post natal hormonal surge of gonadotropins along with testosterone or oestrogen is absent in babies with KS / CHH. This lack of detectable hormones in the blood can be used as a diagnostic indicator, especially in male infants.[30]

In females diagnosis is sometimes further delayed as other causes of amenorrhoea normally have to be investigated first before a case of KS/CHH is considered.[31]

In males the use of age appropriate levels of testosterone can help to distinguish between a case of KS / CHH from a case of delayed puberty. If no puberty is apparent, especially no testicular development, then a review by a reproductive endocrinologist may be appropriate. If puberty is not apparent by the age of 16 then the person should be referred for endocrinological review.[32]

Diagnosis of KS / CHH normal involves a range of clinical, biochemical and radiological tests to exclude other conditions that can cause similar symptoms.

Clinical tests[edit]


Lab tests[edit]


Medical imaging[edit]



Treatment for KS and other forms of HH can be divided into hormone replacement therapy and fertility treatments.[33][26][27][34]

Hormone replacement therapy[edit]

Testosterone gel sachets, Testosterone undecanoate injection (Nebido), Human chorionic gonadotropin (hCG) injection, Menotropin injection (hMG).

For males with KS / CHH the types of testosterone delivery include daily patches, daily gel use, daily capsules, sub cutaneous or intramuscular injections or six monthly implants. Different formulations of testosterone are used to ensure both the anabolic and androgenic effects of testosterone are achieved.[3][4]

For females hormone replacement involves the use of oestrogen and progesterone. In females oestrogen only is used first before a combination of oestrogen and progesterone.[3]

For both males and females the initial aim for treatment is the development of the majority of the secondary sexual characteristics normally seen at puberty. Once this has been achieved continued hormone replacement therapy is required for both males and females to maintain sexual function, bone health, libido and general wellbeing.[3]In males testosterone replacement therapy is required for the maintenance of normal muscle mass.[2]

For both males and females standard hormone replacement therapy will not induce fertility or testicular growth in males.[3]

Fertility treatments[edit]

Gonadotropin therapy can be used in both male and female patients in order to achieve fertility for some people.[3][2]

Pulsatile GnRH therapy can also be used to induce fertility, especially in females but its use is limited to a few specialist treatment centres.[2]


Reversal of symptoms have been reported in between 15% to 22% of cases.[35]

Reversal cases have been seen in cases of both KS and normosmic CHH but appear to be less common in cases of KS (where the sense of smell is also affected).[36]


The epidemiology of Kallmann's is not well understood. Individual studies include a 1986 report reviewing medical records in the Sardinian army found a prevalence of 1 in 86,000 men[37] and a 2011 report from Finland found a prevalence of 1:30,000 for males and 1:125,000 for females.[38]

It occurs about 4 times more often in males than females. However, in familial cases it is only 2.5 time more common in males.[37][38]


Franz J. Kallmann

Kallmann syndrome was first described by name in a paper published in 1944 by Franz Josef Kallmann, a German-American geneticist.[39][40] The link between anosmia and hypogonadism had already been noted by the Spanish doctor Aureliano Maestre de San Juan in 1856.[9] In the 1950s De Morsier and Gauthier reported the partial or complete absence of the olfactory bulb in the brains of men with hypogonadism.[41][11]

Society and culture[edit]


The terminology used when describing cases of HH can vary, other terms used to describe the condition include:


Kisspeptin is a protein that regulates the release of GnRH from the hypothalamus, which in turn regulates the release of LH and to a lesser extent, FSH from the anterior pituitary gland. Kisspeptin and its associated receptor KISS1R are known to be involved in the regulation of puberty. Studies have shown there is potential for kisspeptin to be used in the diagnosis and treatment of conditions such as Kallmann syndrome and CHH in certain cases.[43][44]


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